1. Field of the Invention
The present invention relates to a recording head, and more particularly a recording head which performs a recording operation by ejecting ink toward a recording medium.
2. Description of the Related Art
FIGS. 5A and 5B are schematic diagrams illustrating a portion of a nozzle section in an inkjet recording head according to a related art. FIG. 5A is a plan view, seen through an orifice plate, of the portion of the nozzle section, and FIG. 5B is a sectional view of FIG. 5A taken along line VB-VB.
The inkjet recording head shown in FIGS. 5A and 5B includes an ink supply port 305 through which the ink is supplied to ink passages 303 and a common liquid chamber 304 which communicates with the ink supply port 305. Electrothermal transducers 300 which generate bubbles of ink to eject the ink and pressure chambers 302 in which the electrothermal transducers 300 are disposed are arranged on either side of the common liquid chamber 304. The pressure chambers 302 and the electrothermal transducers 300 are positioned such that the center of gravity of each pressure chamber 302 coincides with the center of gravity of the corresponding electrothermal transducer 300. The ink passages 303 are disposed between the common liquid chamber 304 and the pressure chambers 302, and ink ejection orifices 301 are provided at positions where the ink ejection orifices 301 face the corresponding electrothermal transducers 300.
In this inkjet recording head, the positions of the ink ejection orifices 301 and the electrothermal transducers 300 which are next to each other are shifted from each other in a printing direction (direction in which the carriage is moved) by an amount corresponding to a distance by which the carriage moves within a time interval between times at which respective driving blocks are driven. Since the electrothermal transducers 300 which are next to each other are not driven simultaneously, a so-called crosstalk can be reduced.
For simplicity of explanation, FIG. 5A shows the inkjet recording head in which the nozzles are assigned to four driving blocks and the positions at which the ink ejection orifices 301 are arranged in the printing direction cyclically vary with a period of four nozzles. If the driving blocks are numbered in ascending order from the driving block which is driven first, the upper right ink ejection orifice 301 is assigned to driving block 1 in the example shown in FIG. 5A. The ink ejection orifice 301 on the left side of the upper right ink ejection orifice 301 is assigned to driving block 2, the next ink ejection orifice 301 is assigned to driving block 3, and the next ink ejection orifice 301 is assigned to driving block 4. In the above-described structure, the driving blocks 1 to 4 are successively driven in the ascending order to cause the respective ink ejection orifices 301 to eject ink droplets. Accordingly, the thus-ejected ink droplets land on the recording medium on a straight line.
The above-described structure in which the positions of the ink ejection orifices and the electrothermal transducers are shifted from each other in the printing direction (direction in which the carriage is moved) is described in, for example, Japanese Patent Laid-Open No. 6-238904.
In the above-described inkjet recording head, it is important to eject the ink in a direction substantially perpendicular to the electrothermal transducers and to maintain the manner in which the ink is ejected. If the manner in which the ink is ejected in a direction substantially parallel to the electrothermal transducers cannot be maintained, small droplets (satellite droplets), which are generated together with the main droplets, collide with wall surfaces of the ink ejection orifices and are collected in areas near the ink ejection orifices. Then, when the volume of the ink collected on the surfaces of the ink ejection orifices reaches a certain volume, the collected ink interferes with the ink ejected from the ink ejection orifices and affects the ink ejection state.
To avoid this, Japanese Patent Laid-Open No. 2002-248769 discusses a structure in which the centers of gravity of the ink ejection orifices are offset from the centers of gravity of the electrothermal transducers. FIGS. 6A and 6B show a portion of a nozzle section in which the centers of gravity of the ink ejection orifices are offset from the centers of gravity of the electrothermal transducers. FIG. 6A is a plan view, seen through an orifice plate, of the portion of the nozzle section, and FIG. 6B is a sectional view of FIG. 6A taken along line VIB-VIB. In FIGS. 6A, and 6B, the center lines of ink passages 403 are at positions offset from the center lines of the electrothermal transducers 400. In addition, the centers of gravity of ink ejection orifices 401 are offset from the centers of gravity of the electrothermal transducers 400 in a direction away from an ink supply port 405. According to Japanese Patent Laid-Open No. 2002-248769, the collection of ink in the areas near the ink ejection orifices can be prevented by the above-described structure.
The inventors of the present invention have conducted experiments with different amounts of offsets between the centers of gravity of the ink ejection orifices and the centers of gravity of the electrothermal transducers in the structure in which the distances between the common liquid chamber and the electrothermal transducers in the nozzles which are next to each other differ from each other. As a result, the inventors have newly found that the occurrence status of print defects caused by the above-described collection of ink varies in accordance with the distance between the ink supply port and the electrothermal transducers. The experiments have been conducted using nozzles A and B which are next to each other and in which the distances between the ink supply port and the electrothermal transducers differ from each other. As a result, no print defects have occurred in either of the nozzles A and B when the offset between the centers of gravity of the ink ejection orifices and the centers of gravity of the electrothermal transducers was set to a certain value. However, when the offset was set to another value, print defects have occurred only in the nozzle B. In addition, when the offset between the centers of gravity of the ink ejection orifices and the centers of gravity of the electrothermal transducers was equal to or more than a certain value, the ink ejection characteristics greatly varied and print defects due to causes other than the collection of ink have occurred.